During exercise, the peak LV filling rate in early diastole increases as the duration of diastole decreases with exercise induced tachycardia and stroke volume is maintained or increased. Our studies in conscious instrumented animals indicate that this increased rate of diastolic filling during exercise results from an increased mitral valve pressure gradient produced by a fall in LV early diastolic pressure. This fall in LV early diastolic pressure is associated with a downward shift of the early diastolic portion of the left ventricular pressure volume loop and enhanced rate of left ventricular relaxation during exercise. This is altered after the induction of pacing induced heart failure The early diastole filling rate still increases as does the early diastolic left atrial left ventricular pressure gradient during exercise after CHF. However, this increased pressure gradient results entirely from an increase in left atrial pressure after heart failure. In addition, left ventricular relaxation is not enhanced but in fact is slowed during exercise after heart failure because early diastolic left ventricular pressure does not fall during exercise but actually increases.